Various solutions are known in the art for reducing or eliminating the combustion of polymers. Some of these solutions are based on the use of metals derivatives, especially antimony, bismuth or arsenic, combined with partially halogenated and thermically unstable organic compounds such as paraffinic chlorinated waxes. Other solutions are based on the use of substances capable of producing intumescence. The formulations of products using such substances are generally constituted of the polymer and at least three main additives: one essentially phosphorated, the aim of which is to give, in combustion, an impermeable semisolid glassy layer consisting essentially of polyphosphoric acid and to activate the intumescence process; a second additive containing nitrogen which acts as a foaming agent, and a third additive containing carbon, which provides the carbon necessary for forming a char layer between the polymer and the flame.
Examples of such formulations are those referred to in the following patents: U.S. Pat. No. 3,810,862 (Phillips Petroleum Co.) based on melamine, pentaeritritol and ammonium polyphosphate, U.S. Pat. No. 4,727,102 (Vamp S.r.1.) based on melamine cyanurate a hydroxyalkyl derivative of isocyanuric acid, and ammonium polyphosphate; and in the published patent application WO 85/05626 (Plascoat U.K. Ltd) based on various phosphorus and nitrogen derivatives, including, in particular, a combination of melamine phosphate, pentaerythritol and ammonium polyphosphate. In more recent formulations, an organic compound containing nitrogen, generally an aminoplastic resin obtained by the condensation of urea, melamine or dicyandiamide with formaldehyde, has been used together with an organic or inorganic phosphorous derivative. Examples of formulations with two additives are referred to in patents U.S. Pat. No. 4,504,610 (Montedison Spa) based on oligomeric derivatives of 1,3,5-triazine and ammonium polyphosphate, and EP 14.463 (Montedison Spa), based on organic compounds chosen among benzylguanamine and reaction products of aldehydes and various cyclic nitrogen-substituted compounds, in particular benzylguanamine and formaldehyde copolymers, and of ammonium polyphosphate. It is also possible to obtain self-extinguishing compositions by using mono component additives, containing both nitrogen and phosphorus in the organic molecule as described in U.S. Pat. No. 4,201,705 (Borg-Warner Corp.)
These flame-retardant, intumescent systems give the polymer in which they are contained the property of forming a carbon residue following combustion or contact with a flame. The flame-retardant systems of this kind show numerous advantages: non-corrosion of the machinery used to process the polymers, lower smoke emission compared to systems containing metal derivatives and halogenated hydrocarbons and, above all, the possibility of giving the polymers satisfactory flame-retardant properties using a lower quantity of additive, consequently avoiding a high decrease in the mechanical properties of the polymers.
The Applicant has now discovered that high flame-retardant properties can be conferred to polymers by using mono-components additives which allow to obtain polymeric compositions free of ammonium or amine phosphates and/or phosphonates, or excellent flame-retardant properties by using, with the above additives, a much lower quantity of ammonium or amine phosphates and/or phosphonates than that used in traditional methods.
The Applicant has also discovered that these excellent results can be obtained by using phosphorus-nitrogen containing products having a simple structure, based on polycondensates of 2,4,6-triamino-1,3,5-triazine salified with a phosphorus containing acid. The new additives, moreover, show good stability to heat, thus maintaining a high flame-retardant activity even when the polymeric compositions in which they are contained are processed under heat.
As said before, saline derivatives of 2,4,6-triamino-1,3,5-triazine (melamine) containing phosphors, are known (published patent application WO 85/05626) which can be used as co-additives for self-extinguishing compositions in various polymeric matrices, particularly polyolefines. These compounds, such as the melamine phosphate and melamine pyrophosphate, in order to act as flame-retarardant agents, need the presence of other additives, mainly of a compound containing carbon which is necessary for forming an insulating char layer, such as a polyol (pentaerythritol, dipentaerythritol, tripentaerythritol).
On the contrary, the compounds of the present invention are used in formulations of polymeric materials as intumescent char-forming flame-retardant additives without the help of other components.
The polymeric compositions containing the phosphorusnitrogen. products of the present invention, also have the advantage of emitting a very moderate and not darkening smoke emission in the event of fire.